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Tuning, timing and fueling - can't seem to get it right.

I've had Moe Bailey, Solomon, PCM4Less, PCM Performance, and one other place try to tune this car. Without exception, every single one of them produces loads of ignition knock or ping between 2500 and 3500. I've been able to eliminate the knock now, but I've had to pull gigantic gobs of timing out of the tune. Looking at the datalogs, it would appear that everything is going pretty well with the 02's doing what they need to do and all the sensors reading correctly, but having to yank 8 degrees of timing out of the midrange cells seems like something else is going wrong. All engine electronics are less than 2 years old, including NOS GM Opti, engine itself is about a year old, injectors are 2 years old.

The only thing I can't get rid of is the split BLM's at idle, but it's not pegged. Its like 8-10 points between sides.

I am wondering if I add some fueling to the midrange, will that decrease the knock and let me run more timing? Do I even bother if the car seems to like what I've been able to do? I drove it around the other day with one of the old tunes with more timing and the car definitely had more power, but had so much audible knock I only ran it for 5 minutes and flashed it out.